This excerpt from the 1833 Nautical Almanac demonstrates the use of astronomical symbols, including symbols for the phases of the moon, the planets, and zodiacal constellations.

"Designation of celestial bodies" in a German almanac printed in 1850[1]

Astronomical symbols are abstract pictorial symbols used to represent astronomical objects, theoretical constructs and observational events in Europeanastronomy. The earliest forms of these symbols appear in Greek papyrus texts of late antiquity. The Byzantine codices in which many Greek papyrus texts were preserved continued and extended the inventory of astronomical symbols.[2][3] New symbols were further invented to represent many newly-discovered planets and minor planets discovered in the 18th to the 20th centuries.

These symbols were once commonly used by professional astronomers, amateur astronomers, alchemists, and astrologers. While they are still commonly used in almanacs and astrological publications, their occurrence in published research and texts on astronomy is relatively infrequent,[4] with some exceptions such as the Sun and Earth symbols appearing in astronomical constants, and certain zodiacal signs used to represent the solstices and equinoxes.

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The use of astronomical symbols for the Sun and Moon dates to antiquity. The forms of the symbols that appear in the original papyrus texts of Greek horoscopes are a circle with one ray () for the Sun and a crescent for the Moon.[3] The modern Sun symbol, a circle with a dot (☉), first appeared in Europe in the Renaissance.[3]

In modern academic usage, the Sun symbol is used for astronomical constants relating to the Sun.[7] Teff☉ represents the solar effective temperature, and the luminosity, mass, and radius of stars are often represented using the corresponding solar constants (L☉, M☉, and R☉, respectively) as units of measurement.[8][9][10][11]

Symbols for the classical planets appear in many medieval Byzantine codices in which many ancient horoscopes were preserved.[2] The written symbols for Mercury, Venus, Jupiter, and Saturn have been traced to forms found in late Greek papyrus texts.[22] The symbols for Jupiter and Saturn are identified as monograms of the corresponding Greek names, and the symbol for Mercury is a stylized caduceus.[22] According to A. S. D. Maunder, antecedents of the planetary symbols were used in art to represent the gods associated with the classical planets; Bianchini's planisphere, produced in the 2nd century,[23] shows Greek personifications of planetary gods charged with early versions of the planetary symbols: Mercury has a caduceus; Venus has, attached to her necklace, a cord connected to another necklace; Mars, a spear; Jupiter, a staff; Saturn, a scythe; the Sun, a circlet with rays radiating from it; and the Moon, a headdress with a crescent attached.[24]

A diagram in Byzantine astronomer Johannes Kamateros's 12th century Compendium of Astrology shows the Sun represented by the circle with a ray, Jupiter by the letter zeta (the initial of Zeus, Jupiter's counterpart in Greek mythology), Mars by a shield crossed by a spear, and the remaining classical planets by symbols resembling the modern ones, without the cross-mark seen in modern versions of the symbols. These cross-marks first appear around the 16th century. According to Maunder, the addition of crosses appears to be "an attempt to give a savour of Christianity to the symbols of the old pagan gods."[24]

The symbols for Uranus were created shortly after its discovery. One symbol, , invented by J. G. Köhler and refined by Bode, was intended to represent the newly discovered metal platinum; since platinum, commonly called white gold, was found by chemists mixed with iron, the symbol for platinum combines the alchemical symbols for iron, ♂, and gold, ☉.[25][26] This symbol also combines the symbols of Mars (♂) and the Sun (☉) because in Greek mythology Uranus represented heaven, and represents the combined power of Mars's spear and the Sun.[27]
Another symbol, , was suggested by Lalande in 1784. In a letter to Herschel, Lalande described it as "un globe surmonté par la première lettre de votre nom" ("a globe surmounted by the first letter of your name").[28]

The International Astronomical Union discourages the use of these symbols in journal articles. In certain cases where planetary symbols might be used, such as in the headings of tables, the IAU Style Manual permits certain one- and (to disambiguate Mercury and Mars) two-letter abbreviations for the names of the planets.[36]

Following the discovery of Ceres in 1801 by the astronomer and Catholic priest Giuseppe Piazzi, a group of astronomers ratified the name, which Piazzi had proposed. At that time, the sickle was chosen as a symbol of the planet.[40]

The symbol for 2 Pallas, the spear of Pallas Athena, was invented by Baron Franz Xaver von Zach, who organized a group of twenty-four astronomers to search for a planet between the orbits of Mars and Jupiter. The symbol was introduced by von Zach in his Monatliche correspondenz zur beförderung der erd- und himmels-kunde.[41]
In a letter to von Zach, discoverer Heinrich Wilhelm Matthäus Olbers (who had named the newly discovered asteroid) expressed his approval of the proposed symbol, but wished that the handle of the sickle of Ceres had been adorned with a pommel instead of a crossbar, to better differentiate it from the sign of Venus.[41]

German astronomer Karl Ludwig Harding created the symbol for 3 Juno. Harding, who discovered this asteroid in 1804, proposed the name Juno and the use of a scepter topped with a star as its astronomical symbol.[42]

The symbol for 4 Vesta was invented by German mathematician Carl Friedrich Gauss. Dr. Olbers, having previously discovered and named 2 Pallas, gave Gauss the honor of naming his newest discovery. Gauss decided to name the new asteroid for the goddess Vesta, and also designed the symbol (): the altar of the goddess, with the sacred fire burning on it.[43][44][45] Other contemporaneous writers use a more elaborate symbol () instead.[46][47]

Johann Franz Encke made a major change in the Berliner Astronomisches Jahrbuch (BAJ, Berlin Astronomical Yearbook) for the year 1854, published in 1851. He introduced encircled numbers instead of symbols, although his numbering began with Astraea, the first four asteroids continuing to be denoted by their traditional symbols. This symbolic innovation was adopted very quickly by the astronomical community. The following year (1852), Astraea's number was bumped up to 5, but Ceres through Vesta would be listed by their numbers only in the 1867 edition. The circle later became a pair of parentheses, and the parentheses were sometimes omitted altogether over the next few decades.[14]

A few asteroids were given symbols by their discoverers after the encircled-number notation became widespread. 26 Proserpina, 28 Bellona, 35 Leukothea, and 37 Fides, all discovered by German astronomer Robert Luther between 1853 and 1855, were assigned, respectively, a pomegranate with a star inside;[62] a whip and spear;[63] an antique lighthouse;[64] and a cross.[65]29 Amphitrite was named and assigned a shell for its symbol by George Bishop, the owner of the observatory where astronomer Albert Marth discovered it in 1854.[66]

Pluto's name and symbol were announced by the discoverers on May 1, 1930.[67]
The symbol, a monogram of the letters PL, could be interpreted to stand for Pluto or for Percival Lowell, the astronomer who initiated Lowell Observatory's search for a planet beyond the orbit of Neptune.[12][68]

The zodiac symbols have several astronomical interpretations. Depending on context, a zodiac symbol may denote either a constellation, or a point or interval on the ecliptic plane.

Lists of astronomical phenomena published by almanacs sometimes included conjunctions of stars and planets or the Moon; rather than print the full name of the star, a Greek letter and the symbol for the constellation of the star was sometimes used instead.[75][76] The ecliptic was sometimes divided into 12 signs, each subdivided into 30 degrees,[77][78] and the sign component of ecliptic longitude was expressed either with a number from 0 to 11[79] or with the corresponding zodiac symbol.[78]

In modern academic usage, all the constellations, including the twelve of the zodiac, have dedicated three-letter abbreviations.[80] The zodiac symbols are also sometimes used to represent points on the ecliptic, particularly the solstices and equinoxes. Each symbol is taken to represent the "first point" of each sign.[81][82] Thus, ♈︎ the symbol for Aries, represents the March equinox; ♋︎, for Cancer, the June solstice; ♎︎, for Libra, the September equinox; and ♑︎, for Capricorn, the December solstice.

Symbols for aspects and nodes appear in medieval texts, although medieval and modern usage of the node symbols differ; the modern ascending node symbol (☊) formerly stood for the descending node, and the modern descending node symbol (☋) was used for the ascending node.[3] In describing the Keplerian elements of an orbit, ☊ is sometimes used to denote the ecliptic longitude of the ascending node, although it is more common to use Ω (capital omega), which was originally a typographical substitute for the astronomical symbol.[84]

The symbols for aspects first appear in Byzantine codices.[3] Of the symbols for the five Ptolemaic aspects, only the three displayed here—for conjunction, opposition, and quadrature—are used in astronomy.[85]

Symbols for a comet (☄) and a star () have been used in published astronomical observations of comets. In tables of these observations, ☄ stood for the comet being discussed and for the star of comparison relative to which measurements of the comet's position were made.[86]

^Goswami, Aruna (2010). Principles and Perspectives in Cosmochemistry: Lecture Notes of the Kodai School on 'Synthesis of Elements in Stars' Held at Kodaikanal Observatory, India, April 29 - May 13, 2008. pp. 4–5.

^Gray, David F. (2005). The observation and analysis of stellar photospheres. Cambridge University Press. p. 505.

^"Bianchini's planisphere". Florence, Italy: Istituto e Museo di Storia della Scienza (Institute and Museum of the History of Science). Archived from the original on February 27, 2018. Retrieved August 20, 2018.

^ abFaulks, David (May 9, 2006). "Proposal to add some Western Astrology Symbols to the UCS"(PDF). p. 4. Archived(PDF) from the original on June 15, 2018. Retrieved November 20, 2017. In general, only the signs for Vesta have enough variance to be regarded as different designs. However, all of these Vesta symbols ... are differing designs for 'the hearth and flame of the temple of the Goddess Vesta' in Rome, and can thus be regarded as extreme variants of a single symbol.

^ ab"Extract of a Letter from Mr. Graham". Monthly Notices of the Royal Astronomical Society. 8: 147. 1848. I trust, therefore, that astronomers will adopt this name [viz. Metis], with an eye and star for symbol.

^ abHind (1851). "On the Discovery of a Fourth New Planet, at Mr. Bishop's Observatory, Regent's Park". Monthly Notices of the Royal Astronomical Society. 11 (8): 171. doi:10.1093/mnras/11.8.170a. Sir John Herschel, who kindly undertook the selection of a name for this, the fourteenth member of the ultra-zodiacal group, has suggested Irene as one suitable to the present time, the symbol to be a dove carrying an olive-branch with a star on the head; and since the announcement of this name, I have been gratified in receiving from all quarters the most unqualified expressions of approbation.